1. Field of the Invention
The present invention relates to a process for preparing a block or comb copolymer comprising at least one hydrophilic portion and at least two hydrophobic portions, as well as to copolymers obtained by this process.
The aim of the process of the invention is preparing block or comb copolymers comprising hydrophilic segments carrying hydroxyl groups, and polylactone type hydrophobic segments. Such copolymers are known to be biodegradable and non toxic copolymers which are capable of forming micelles in the aqueous phase.
2. Description of the Related Art
International patent application WO-A-97/19973 and Rashkov et al (Macromolecules 1996, 29, pp 50-56) describe the solvent-free copolymerization of polyethylene glycol and lactone. The process comprises steps consisting of degassing the reaction mixture (placed in a flask) under vacuum, heating it in an atmosphere of argon to 140° C. until the mixture is in the liquid form, then placing it under a vacuum of 10−2 mm/Hg and sealing the flask then keeping it in an oven at 140° C. for 7 days. The reaction is carried out in the presence of calcium hydride acting as a catalyst. However, in that process, a high performance degassing apparatus is needed in order to be able to operate under a partial vacuum. Installing and operating such an apparatus complicates the synthesis process in the laboratory (Schlenk apparatus, sealing, sealed tubes, vacuum pumps, etc), but far more so on an industrial scale for greater production. Such apparatus is costly and constitutes an obstacle to operating such a process on the industrial scale.